The present invention relates to synchronous networks, and to the carrying of frame based data over synchronous networks.
In the applicant""s co-pending patent application entitled xe2x80x9cFrame Based Data Transmission over Synchronous Digital Hierarchy Networkxe2x80x9d filed contemporaneously with the present application, and a copy of which is filed herewith, there is disclosed a method of carrying frame based data over a synchronous digital network. Such disclosed system may provide OSI layer 2 switching functionality which was only previously available in prior art local area networks, but extended over a geographical coverage area which has been historically considered to have been provided only by prior art wide area networks.
In order to accommodate datacoms frame based data, which is characterized by its own set of data rates and control data characteristics, and to contain such frame based data in conventional synchronous digital networks, there is a problem that the frame based datacoms data rates are not well matched to conventional telecoms data rates, for example E1, E3, T1, STM-1 data rates.
Several prior art attempts have been made to carry datacoms services including frame based data over telecoms networks. Prior art systems for incorporating frame based data over synchronous networks include schemes which contain Ethernet data frames in asynchronous transfer mode (ATM) cells which are then transported in a plesiochronous mode and which may then be transported according to ITU-T recommendation G.708 in a synchronous digital hierarchy (SDH) network. In this scheme, known as Inverse Multiplexing of ATM (IMA), conceived by the ATM Forum, an ATM circuit is divided by multiplexing individual ATM cells, which are input into a plurality of E1 circuits. This enables an ATM signal to be carried across a legacy network, for example a plesiochronous digital hierarchy (PDH) network. Ethernet frames are included as the payload of the ATM cells, which are then carried via the E1 circuits over a conventional PDH network which can be carried over an SDH network. A protocol stack for an inverse multiplexing of ATM scheme between first and second physical resources A and B carried over a synchronous digital network channel 100 is illustrated in FIG. 1 herein. Internet protocol packets (IP) are encapsulated using request for comment (RFC) 1483 protocol into asynchronous transfer mode cells. RFC 1483 is published by Internet Engineering Task Force, the location and Internet address of which is well known to those skilled in the art. The ATM cells are then inverse multiplexed, by dividing them up and entering them into ITU-T G.703 plesiochronous digital hierarchy bitstreams, which are then carried in virtual containers over a synchronous digital hierarchy synchronous channel 100. De-layering of the SDH payloads at the receiving entity is achieved as a reverse of layering of the Internet protocol packets. However, this prior art scheme has a disadvantage of a high packetization header overhead, which can comprise up to 20% of the SDH payload. Each layer of packetization and encapsulation also adds delay to the data traffic carried.
Other prior art attempts at carrying frame based data over synchronous networks include a system known as media independent interface, produced by CISCO and a similar system produced by Bay Networks. Another prior art system aimed at carrying frame based data over synchronous digital network is the Packet On Site (POS phy) system of PMC Sierra. However, in each of these schemes, a high packetization overhead is present and packaging delays are relatively high, which slows down passage of datacoms data through a network.
One object of the present invention is to provide a means and method for efficiently mapping datacoms type data produced at frame based data rates in packetized format, into a synchronous digital virtual container system for transport of the frame based data over a synchronous digital network.
Ideally, frame based data is incorporated into a synchronous digital network with a minimum packing delay in containing the frame based data in the synchronous digital containers.
A further object of the present invention is to multiplex a plurality of frame based data channels, into a synchronous digital network channel.
A further object of the present invention is to achieve containment of frame based data directly into synchronous digital network containers, with a minimum protocol header overhead.
According to one aspect of the present invention there is provided a method for transporting frame based packet data into a synchronous transmission communications network, said method comprising the steps of:
encoding at least one packet data frame with a code which designates a boundary of said frame;
inputting said encoded packet data frame into a synchronous data channel.
The synchronous communications protocol, for example SDH protocol under ITU-T recommendation G.70X recognizes the code as marking a boundary of a packet data frame.
Said step of encoding at least one packet data frame may comprise:
appending a fixed pointer describing a position of a said boundary within a data stream containing said packet data frame, said fixed pointer appended into said synchronous digital channel.
A said fixed pointer comprises a pointer designating an end of said packet data frame, or a start of said packet data frame.
The pointer preferably designates a position of a said boundary within a synchronous virtual container, of a synchronous network.
The step of encoding at least one packet data frame may alternatively comprise:
partitioning said packet data frame into a plurality of bytes;
for each byte appending an extra bit indicating that said corresponding respective byte comprises part of said packet data frame; and
for a last byte of said packet data frame, appending an extra bit indicating that said byte constitutes a last byte of said data frame.
The step of encoding at least one packet data frame may comprise applying a consistent overhead byte stuffing algorithm to said data frame.
This may have an advantage that an encoding delay incurred by encoding the packet data frame with the byte stuffing algorithm is of known and predetermined duration.
Said step of encoding at least one packet data frame may comprise:
applying a coding algorithm to said packet data frame which identifies a boundary of said data frame by appending a fixed number of bits to said data frame, irrespective of a size of said data frame.
Said step of encoding at least one packet data frame may comprise:
applying a coding algorithm to said data frame which identifies a boundary of said data frame by appending a fixed number of bits to said data frame, irrespective of a data content of said data frame.
Preferably said step of inputting said encoded packet data frame into a synchronous data channel comprises inputting said data frame into at least one virtual container.
According to a second aspect of the present invention there is provided a method of receiving frame based data carried in a synchronous transmission communications network comprising the steps of:
recovering a stream of encoded data from a synchronous digital channel;
identifying in said recovered data stream at least one marker designating a boundary of a data frame; and
using said marker to recover said data frame from said data stream.
According to a third aspect of the present invention there is provided a method of carrying packet data frames over a synchronous digital hierarchy network, said method comprising the steps of:
delineating a plurality of said data frames from a received packet data frame bit sequence;
marking at least one boundary of each said packet data frame; and
incorporating each said encoded, marked packet data frame into at least one synchronous virtual container.
According to a fourth aspect of the present invention there is provided a method of decoding encoded packet frame data.
According to a fifth aspect of the present invention there is provided apparatus for incorporating frame based data into a synchronous transmission communications network, said apparatus comprising:
means for encoding a plurality of data frames with a plurality of markers designating boundaries of said data frames; and
means for multiplexing said encoded data frames into a synchronous virtual container.
The invention includes a method of encoding frame based data into a format suitable for inclusion into a virtual container of a synchronous digital network, said method comprising the steps of:
dividing said packet data frame into a plurality of data blocks, each having a predetermined number of bits;
for each said data block, appending an extra bit to said data block, said extra bit designating that said data block comprises said packet data frame; and
for a last data block of a said packet data frame, appending a second bit, said second bit designating said last data block as an end of said packet data frame.
The invention includes a method of decoding an encoded digital bitstream to recover a plurality of packet data frames, said method comprising the steps of:
receiving a digital bitstream comprising a plurality of data blocks, each said data block having an additional appended bit designating whether said data block belongs to a packet data frame or not;
for each said data block, checking said extra bit to determine whether said corresponding respective data block belongs to a packet data frame or not;
for each said data block, removing said appended extra bit; and
for each of a plurality of data blocks having a bit designating said data block belongs to a packet data frame, assembling said data blocks into a said data frame.